System and method for sensing battery capacity

ABSTRACT

One embodiment of the invention includes a battery sense system. The system includes a temperature sensor configured to measure a temperature of a battery and a memory configured to store predetermined data associated with steady-state and transient behaviors of the battery relative to a depth of discharge (DOD) of the battery. The system also includes a controller configured to measure a voltage of the battery and to calculate a state of charge (SOC) of the battery based on the voltage, the predetermined data, and the temperature.

TECHNICAL FIELD

The invention relates generally to electronic circuits and, morespecifically, to a system and method for sensing battery capacity.

BACKGROUND

Portable electronic devices are powered by batteries that generate avoltage based on chemical reactions. As a battery provides power to theportable electronic device, the capacity of the battery to provide thepower becomes diminished. Some portable electronic devices provideindications of remaining battery capacity, such that the user of theportable electronic device is provided with notice of the remainingbattery capacity. However, such battery sense systems can often beinaccurate and/or can include additional circuit components that can beexpensive, bulky, and/or inefficient with respect to power draw.

SUMMARY

One embodiment of the invention includes a battery sense system. Thesystem includes a temperature sensor configured to measure a temperatureof a battery and a memory configured to store predetermined dataassociated with steady-state and transient behaviors of the batteryrelative to a depth of discharge (DOD) of the battery. The system alsoincludes a controller configured to measure a voltage of the battery andto calculate a state of charge (SOC) of the battery based on thevoltage, the predetermined data, and the temperature.

Another embodiment of the invention method for calculating an SOC of abattery. The method includes modeling the battery as a dynamic batterymodel comprising a steady-state circuit portion and a transient circuitportion to determine predetermined data associated with steady-state andtransient behaviors of the battery relative to a DOD of the battery. Themethod also includes determining a temperature of the battery, measuringa voltage of the battery, and accessing the predetermined data from amemory. The method further includes calculating the SOC of the batterybased on the voltage, the predetermined data, and the temperature.

Yet another embodiment of the invention includes a battery sense system.The system includes a temperature sensor configured to measure atemperature of a battery and a memory configured to store predetermineddata associated with steady-state and transient behaviors of the batteryrelative to a DOD of the battery. The system also includes a controllerconfigured to obtain samples of a voltage of the battery at each of aplurality of sampling intervals, to estimate a corresponding currentgenerated by the battery at a given sampling interval based on thevoltage at a respective one of the sampling intervals, the predetermineddata, and the temperature. The controller is also configured tocalculate an SOC of the battery based on based on the current throughthe battery at the respective one of the sampling intervals and based onthe DOD of the battery at an immediately preceding sampling interval.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a battery sense system in accordancewith an aspect of the invention.

FIG. 2 illustrates an example of a dynamic battery model in accordancewith an aspect of the invention.

FIG. 3 illustrates an example of a graph of voltage versus time inaccordance with an aspect of the invention.

FIG. 4 illustrates an example of a table of dynamic battery model datain accordance with an aspect of the invention.

FIG. 5 illustrates an example of a method for calculating a state ofcharge (SOC) of a battery in accordance with an aspect of the invention.

DETAILED DESCRIPTION

The invention relates generally to electronic circuits and, morespecifically, to a system and method for sensing battery capacity. Abattery sense system can include a temperature sensor that measures atemperature of the battery. The temperature is provided to a batterysense controller that is configured to measure a voltage of the batteryand to calculate a state of charge (SOC) of the battery based on thevoltage, the temperature, and based on predetermined data associatedwith steady-state and transient behavior of the battery. Thepredetermined data can be stored in a memory, which can be accessed bythe battery sense controller at each of a plurality of samplingintervals, such that the SOC of the battery can likewise be determinedat each of the sampling intervals.

As described herein, the SOC of a battery is sometimes used to indicatehow much available charge remains in the battery. The depth of discharge(DOD) of the battery can refer to how much the battery has discharged,and can be defined as a present remaining integrated charge Q divided bya maximum total zero-current charge Q_(MAX) of the battery. The DOD ofthe battery is related to the SOC by the equation DOD+SOC=1, and isusually utilized to obtain a computation of the remaining run-time of adevice powered by the battery. Therefore, as described herein, the SOCand DOD can generally be described in an interchangeable manner based onthe inversely proportional relationship between SOC and DOD with respectto one.

The predetermined data can be generated offline and can correspond tothe particular battery chemistry of the battery being sensed, such as ata time prior to manufacture of the battery, based on modeling thebattery as a dynamic battery model and performing a series of tests on acorresponding test battery. As an example, the dynamic battery model canbe configured to include a steady-state circuit portion and a transientcircuit portion that each includes at least one RC network. For example,an RC network of the steady-state circuit portion can include aseries-connected resistor and capacitor, and an RC network of thetransient circuit portion can include a parallel-connected resistor andcapacitor. The values of the resistors and capacitors in each of therespective static and transient circuit portions can be determined byapplying a predetermined load to the corresponding test battery,determining a change in voltage relative to a responsive current, andremoving the load to determine a voltage response. Furthermore, thevalues of resistance of the battery and the voltage of the steady-statecircuit portion of the dynamic battery model can be temperaturedependent, and can thus likewise be determined on the test battery andincluded in the predetermined data.

The battery sense controller can thus perform a series of calculationsbased on the voltage, the predetermined data, and the temperature of thebattery to determine the SOC of the battery. Specifically, the batterysense controller can iteratively calculate a current of the battery ateach of a plurality of sampling intervals based on the voltage at therespective sampling intervals and the DOD of the previous samplingperiod. The current can then be used to calculate a current SOC of thebattery. Accordingly, the battery sense controller can continue tocalculate new values for the SOC of the battery based on priorcalculations and current measurements of both voltage and temperature.

FIG. 1 illustrates an example of a battery sense system 10 in accordancewith an aspect of the invention. The battery sense system 10 can beincluded as part of any of a variety of portable electronic devices,such as a laptop computer, a camera, or a wireless communicationsdevice. The battery sense system 10 a battery sense controller 12 thatis configured to determine a state of charge (SOC) of a battery 14during operation of the associated portable electronic device.Specifically, the battery sense controller 12 can be configured tocontinuously sample a voltage V_(BAT) of the battery 14 at each of aplurality of sampling periods to provide the SOC of the battery 14 ateach of the sampling periods based on the voltage V_(BAT), a temperatureof the battery 14, predetermined data associated with steady-state andtransient behaviors of the battery 14 relative to a depth of discharge(DOD) of the battery 14. In the example of FIG. 1, the battery 14 isdemonstrated as a single battery. However, it is to be understood thatthe battery 14 can represent a plurality of batteries electricallyconnected in series, such that the voltage V_(BAT) could represent anaggregate voltage of all of the batteries. Therefore, the SOC calculatedby the battery sense controller 12 can be an average SOC of theplurality of batteries.

The battery sense system 10 includes a temperature sensor 16 that isconfigured to provide a temperature signal TEMP to the battery sensecontroller 12. The temperature signal TEMP can be a signal associatedwith an actual temperature of the battery 14, such as based on anexternal sensor coupled directly to the battery 14, or can be a measureof an ambient temperature of an area surrounding the battery. As anexample, the temperature signal TEMP can be a digital signal, such asprovided by an analog-to-digital converter (ADC) that can be part of thetemperature sensor 16. The battery sense system 10 also includes amemory 18 that is configured to store battery model data 20 and previousbattery data 22. The battery model data 20 includes steady-statebehavior data 24 corresponding to steady-state behavior parameters ofthe battery 14 and transient behavior data 26 corresponding to transientbehavior parameters of the battery 14. As described in greater detailbelow, the steady-state behavior data 24 and the transient behavior data26 can include data regarding a dynamic battery model having values thatare dependent on the DOD of the battery 14.

The battery model data 20 can be generated offline, such as at a timeprior to manufacture of the battery 14, by conducting tests on a testbattery (not shown) having substantially the same chemistry as thebattery 14. The characteristics of a given battery, as dependent on DOD,are generally applicable to all batteries having a particular chemistry.For example, a comparison of an open circuit voltage V_(OC) of a givenbattery relative to a DOD for four different batteries, each having thesame chemistry, from four different manufacturers shows that the opencircuit voltages V_(OC) of each of the batteries do not differ by morethan approximately 5 millivolts, so the same database can be used forall batteries of the same chemistry (e.g., lithium ion). Thus, thebattery model data 20 can correspond to data associated with a batteryof substantially the same chemistry as the battery 14, such that thebattery model data 20 can be implemented to provide an accuratecalculation of the SOC of the battery 14. Accordingly, the battery sensecontroller 12 can implement the battery model data 20, provided from thememory 18 via a signal DATA_(MODEL), to calculate the SOC of the battery14.

The previous battery data 22 is a set of data corresponding to priorcalculations of data regarding the battery 14. As an example, theprevious battery data 22 can include a previously calculated DOD of thebattery 14, a previously measured voltage V_(BAT), and a previouslyestimated battery current. In the example of FIG. 1, upon the batterysense controller 12 calculating the DOD of the battery 14, the batterysense controller 12 can provide the DOD and additional data required forthe calculation to the memory 18 as a signal DATA_(BAT) to be stored asthe previous battery data 22. Thus, upon the battery sense controller 12calculating a next DOD value of the battery 14, the battery sensecontroller 12 can receive the previous battery data 22 via a signalDATA_(PREV), provided from the memory 18, to implement the previousbattery data 20 to calculate the SOC of the battery 14. Accordingly, asdescribed in greater detail below, the battery sense controller 12 cancalculate a current SOC of the battery 14 based on the voltage V_(BAT),the temperature of the battery 14, indicated by the temperature signalTEMP, the battery model data 20, indicated by the signal DATA_(BAT), andthe previous battery data 22, indicated by the signal DATA_(PREV).

As described above, the battery model data 20 can be generated for thebattery 14 based on modeling the battery 14 as a dynamic battery model.FIG. 2 illustrates an example of a dynamic battery model 50 inaccordance with an aspect of the invention. The dynamic battery model 50can correspond to the battery 14 in the example of FIG. 1. Therefore,reference is to be made to the example of FIG. 1 in the followingdescription of the example of FIG. 2.

The dynamic battery model 50 includes a steady-state circuit portion 52and a transient circuit portion 54 that are each configured as RCnetworks. Specifically, the steady-state circuit portion 52 includes aresistor R_(SER) and a capacitor C_(SER) that are arranged in series andthe transient circuit portion 54 includes a resistor R_(PAR) and acapacitor C_(PAR) that are arranged in parallel. While the example ofFIG. 2 demonstrates a single parallel-coupled RC network for thetransient circuit portion 54, it is to be understood that the transientcircuit portion 54 can include multiple parallel-coupled RC networks,such as connected in series with each other, that collectively model thetransient characteristics of the battery 14. The capacitor C_(SER)corresponds to a voltage source of the dynamic battery model, and isthus modeled as having an associated open-circuit voltage V_(OC) acrossit. The open-circuit voltage V_(OC) thus corresponds to an instantaneoussteady-state voltage of the dynamic battery model 50. Collectively, theresistor R_(SER) and the transient circuit portion 54 constitute abattery impedance between nodes 56 and 58 for the dynamic battery model50 having a resistance R_(BAT). The dynamic battery model 50 also has asample voltage V(t) and an associated sample current I(t) correspondingto instantaneous magnitudes of the voltage and current of the dynamicbattery model 50 at a given sample time.

The dynamic battery model 50 can be used to build a table ofpredetermined data associated with steady-state and transient behaviorsof the battery 14, such as included in the battery model data 20 in theexample of FIG. 1. As an example, during testing for the particularchemistry of the battery 14, a predetermined load (not shown) can beperiodically coupled and decoupled to the corresponding test battery tomeasure a voltage response of the test battery through the life of thetest battery. Therefore, operational characteristics of the battery 14can be obtained at predetermined DOD values of the battery 14. Thus, theoperational characteristics of the battery 14 during the test can beimplemented to determine values for the open-circuit voltage V_(OC), thecapacitance C_(SER), the resistance R_(SER), the capacitance C_(PAR),and the resistance R_(PAR) at each of the predetermined DOD values ofthe battery 14. Such values can then be used to build the battery modeldata 20 as a function of DOD of the battery 14.

FIG. 3 illustrates an example of a graph 100 of voltage versus time inaccordance with an aspect of the invention. The graph 100 can describe avoltage response of the test battery that is associated with the dynamicbattery model 50 in the example of FIG. 2, and thus can be implementedto ascertain values for the open-circuit voltage V_(OC), the capacitanceC_(SER), the resistance R_(SER), the capacitance C_(PAR), and theresistance R_(PAR) at each of the predetermined DOD values of thebattery 14. Thus, reference is to be made to the example of FIGS. 1 and2 in the following example of FIG. 3.

The graph 100 demonstrates the voltage V(t) of the dynamic battery model50 plotted as a function of time. In performing tests on the testbattery, a predetermined load can be applied to and removed from thetest battery at specific DOD intervals of the test battery. The voltageresponse of the test battery can thus be monitored to ascertain thevalues for the open-circuit voltage V_(OC), the capacitance C_(SER), theresistance R_(SER), the capacitance C_(PAR), and the resistance R_(PAR)at each of the DOD intervals. Specifically, at a time T₀, there is noload applied to the test battery, such that the voltage V(t) has a valueV₀ that remains substantially constant.

Subsequent to the time T₀, at a time T₁, the predetermined load isapplied to the test battery, such that a known current I(t) flows fromthe test battery. In response, the voltage V(t) begins to reduce fromthe magnitude V₀ at the time T₁ to a magnitude V₁ at a time T₂, at whichtime the predetermined load is removed from the test battery. The regionof time between the times T₁ and T₂ of the graph 100 can thus define ahigh-frequency region 102 of the voltage V(t), which can thus identifyparameters of the test battery during a given DOD interval X of thehigh-frequency region 102. As an example, the value of the resistorR_(SER) can be identified based on a change in the voltage V(t) relativeto the change in current I(t), such that:R _(SER)(X)=dV(t)/dI(t)  Equation 1Thus, the value of the resistor R_(PAR) can be ascertained as follows:R _(PAR)(X)=R _(BAT)(X)−R _(SER)(X)  Equation 2In addition, for a given DOD interval, the open circuit voltage V_(OC)across the capacitor C_(SER) can be determined based on the voltage V(t)and the as follows:V _(OC)(X)=V(t)−V _(RC)(X)=I(t)*R _(BAT)(X)  Equation 3

Where: V_(RC) is the voltage across the resistance R_(BAT).

Therefore, the high-frequency region 102 of a given DOD interval can beimplemented to determine the values of R_(SER), R_(PAR), and V_(OC) forthe given DOD interval X.

After the time T₂, upon the predetermined load being removed from thetest battery, the voltage V(t) relaxes, and thus increases from themagnitude of V₁ to a magnitude of V₂ in the example of FIG. 3. Thus, thetime T₂ defines a relaxation region 104. The increase in the magnitudeof the voltage V(t) from V₁ to V₂ in the relaxation region 104 can thusbe analyzed to determine an additional parameter of the dynamic batterymodel 50. Specifically, the increase in the voltage V(t) as a functionof time t can determine the magnitude of the capacitance C_(PAR) for theDOD interval X, as follows:C _(PAR)(X)=dV(t)/dt  Equation 4

Upon ascertaining the values for the open-circuit voltage V_(OC), theresistance R_(SER), the capacitance C_(PAR), and the resistance R_(PAR)at each of the DOD intervals, the values for the capacitance C_(SER) canbe determined based on the number Y of DOD intervals for which the testbattery was tested. Specifically, for the DOD interval X, the values forthe capacitance C_(SER) can be determined as follows:

$\begin{matrix}{{C_{SER}(X)} = {\frac{Q_{MAX}}{\left( {Y - 1} \right)}*\left( {{V_{OC}(X)} - {V_{OC}\left( {X - 1} \right)}} \right)}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Where: Q_(MAX) is a maximum total zero-current charge of the testbattery.

Therefore, the circuit parameters of the dynamic battery model 50 can befully modeled for each of the DOD intervals Y.

The initial experimentation to ascertain values for the open-circuitvoltage V_(OC), the capacitance C_(SER), the resistance R_(SER), thecapacitance C_(PAR), and the resistance R_(PAR) at each of thepredetermined DOD values of the battery 14 can be conducted at apredetermined “room” temperature. Thus, based on the temperaturedependence of both the resistance and the voltage of the dynamic batterymodel 50, the experimentation using the test battery in building thebattery model data 20 based on the dynamic battery model 50 can alsoincorporate temperature components. Specifically, as temperature willaffect the resistors R_(SER) and R_(BAT) and the capacitors C_(SER) andC_(PAR) substantially equally, ratios of the magnitudes of the resistorsR_(SER) and R_(BAT) and the capacitors C_(SER) and C_(PAR) can bedeveloped and incorporated as part of the battery model data 20.Specifically, the ratios at each DOD interval X can be defined asfollows:RATIO₁(X)=R _(SER)(X)/R _(PAR)(X)  Equation 6RATIO₂(X)=C _(SER)(X)/C _(PAR)(X)  Equation 7

In addition, based on temperature experimentation on the test battery, aset of factors for calculating the open-circuit voltage V_(OC) and thebattery resistance R_(BAT) based on temperature can be determined.Specifically, the set of DOD dependent variables can allow temperaturedependent calculation of the open-circuit voltage V_(OC) and the batteryresistance R_(BAT) based on the following equations:V _(OC)(X)=OCV_(—) A(X)+OCV_(—) B(X)*T  Equation 8R _(BAT)(X)=R _(—) A(X)^((R) ^(—) ^((X)*(10*T-250)))  Equation 9

Where: T is temperature;

-   -   OCV_A is an intercept variable for the open-circuit voltage        V_(OC);    -   OCV_B is a slope coefficient for the open-circuit voltage        V_(OC);    -   R_A is a base variable for the battery resistance R_(BAT); and    -   R_B is an exponent coefficient for the battery resistance        R_(BAT).        Thus, the battery model data 20 can include values for the        intercept variable OCV_A, the slope coefficient OCV_B, the base        variable R_A, and the exponent coefficient R_B for each of the Y        DOD values. The base variable R_A may have dynamic values, such        that the battery sense controller 12 can update the values of        the base variable R_A (e.g., via the signal DATA_(BAT)) to        account for battery aging, such as based on a comparison of        information associated with the measured voltage V_(BAT), the        open-circuit voltage V_(OC), and an estimated current I_(EST)        (described in greater detail below). Additionally, based on the        differing effects of temperature on the resistance, the exponent        coefficient R_B could include a plurality of values at each of        the DOD values based on different ranges of temperature. As an        example, at a given DOD value X, the battery model data 20 could        include an exponent coefficient R_B_(LOW) for temperatures below        a certain threshold (e.g., 25° C.) and a separate exponent        coefficient R_B_(HIGH) for temperatures above the threshold.

FIG. 4 illustrates an example of a table 150 of the dynamic batterymodel data in accordance with an aspect of the invention. The dynamicbattery model data can correspond to the battery model data 20 in theexample of FIG. 1, and can be generated based on the techniquesdescribed above with respect to the examples of FIGS. 2 and 3.Therefore, reference is to be made to the examples of FIGS. 1 through 3in the following examples of FIG. 4.

The table 150 includes a first column 152 that demonstrates a set of DODvalues for which a given set of the battery model data 20 is ascertainedfrom the test battery and the dynamic battery model 50. In the exampleof FIG. 4, the first column 152 includes 15 different values for the DODof the battery 14. However, it is to be understood that the values ofthe DOD in the example of FIG. 4 are demonstrated as an example, andthat the table 150 could include any number of DOD values for which thebattery model data 20 has been obtained. The table 150 also includes asecond column 154 that demonstrates the intercept variable OCV_A, athird column 156 that demonstrates the slope coefficient OCV_B, and afourth column 158 that demonstrates the base variable R_A. The table 150also includes a fifth column 160 that demonstrates the exponentcoefficient R_B, a sixth column 162 demonstrating the RATIO₁, and aseventh column that demonstrates the RATIO₂. Therefore, the batterymodel data 20 can include a substantially complete characterization ofthe steady-state and transient behaviors of the battery 14 fordetermining the SOC of the battery 14.

Referring back to the example of FIG. 1, at a given sampling time (k),the battery sense controller 12 can thus calculate the SOC of thebattery 14. The battery sense controller 12 can first measure thevoltage V_(BAT)(k) and the temperature T of the battery 14 via thetemperature signal TEMP and can estimate a current I_(EST)(k) of thebattery 14. To estimate the current I_(EST)(k), the battery sensecontroller 12 can access the memory 18 for the previous battery data 22,via the signal DATA_(PREV), to obtain the DOD, the estimated currentI_(EST), and the battery voltage V_(BAT) that were obtained andcalculated at a previous sampling time (k−1). Based on the value of theDOD(k−1), the battery sense controller 12 can access the memory 18 toobtain the battery model data 20 via the signal DATA_(MODEL).Specifically, the battery sense controller 12 can access the parametersfrom the table 150 corresponding to the two known DOD values that areimmediately greater than and immediately less than the DOD(k−1).Therefore, the battery sense controller 12 can determine values for theintercept variable OCV_A, the slope coefficient OCV_B, the base variableR_A, the exponent coefficient R_B, the RATIO₁, and the RATIO₂ based onlinear interpolation of the values at each of DOD(X) and DOD(X+1)between which DOD(k−1) resides. It is to be understood that, for thefirst sampling time (k) after a fully charged battery 14 (i.e., SOC=1),the data of the previous sampling time (k−1) can correspond to thebattery model data 20 of the first value of the DOD (i.e., DOD=0.000).

Upon obtaining the values for the battery model data 20 at the DOD(k−1),the battery sense controller 12 can implement Equations 6 and 9 above toobtain actual values for the modeled resistance R_(SER) and R_(PAR) ofthe battery 14 based on the temperature T. Specifically, using Equation9, the battery sense controller 12 can calculate the total resistance ofthe battery R_(BAT) as adjusted for temperature. Then, using thetemperature adjusted resistance value of the battery R_(BAT), thebattery sense controller 12 can implement Equation 6 as follows:R _(BAT) =R _(SER) +R _(PAR) =R _(PAR) +R _(PAR)*RATIO₁  Equation 10Therefore, the battery sense controller 12 can calculate the modeledresistance R_(SER) and R_(PAR) of the battery 14 as follows:R _(PAR) =R _(BAT)/(1+RATIO₁)  Equation 11R _(SER) =R _(BAT) −R _(PAR)  Equation 12

As described above, the battery sense controller 12 can obtain valuesfor the open-circuit voltage V_(OC) and the capacitance C_(SER) forevery one of the DOD values X based on Equations 3 and 5, respectively.Thus, the battery sense controller 12 can likewise determine the valuesof the open-circuit voltage V_(OC) and the capacitance C_(SER) based onlinear interpolation of the values at each of DOD(X) and DOD(X+1)between which DOD(k−1) resides. The battery sense controller 12 can thencalculate the value of the capacitance C_(PAR) as follows:C _(PAR) =C _(SER)/RATIO₂  Equation 13

The battery sense controller 12 can then use the values calculated forthe resistances R_(SER) and R_(PAR), the capacitance C_(PAR), and theopen-circuit voltage V_(OC) to estimate the current I_(EST)(k).Specifically, the battery sense controller 12 can use the valuescalculated for the resistances R_(SER) and R_(PAR) and the capacitanceC_(PAR) to calculate a set of coefficients for estimating the currentI_(EST)(k). The coefficients can be defined as follows:

$\begin{matrix}{P_{0} = {1/R_{SER}}} & {{Equation}\mspace{14mu} 14} \\{P_{1} = {- {\mathbb{e}}^{\frac{- {Ts}}{({R_{PAR}*C_{PAR}})}}}} & {{Equation}\mspace{14mu} 15} \\{P_{2} = {{\mathbb{e}}^{\frac{- {Ts}}{({R_{PAR}*R_{SER}})}} - {R_{PAR}*\frac{\left( {1 - {\mathbb{e}}^{\frac{- {Ts}}{({R_{PAR}*C_{PAR}})}}} \right)}{R_{SER}}}}} & {{Equation}\mspace{14mu} 16}\end{matrix}$

Where: Ts is a sampling time.

It is to be understood that the coefficients P₀, P₁, and P₂ can becalculated at each sample (k), as described above, or could becalculated during testing at each predetermined DOD(X), such that thevalues of the coefficients P₀, P₁, and P₂ at a given sampling time (k)can be linearly interpolated, similar to as described above.

The battery sense controller 12 can then calculate the voltage V_(RC)across the resistor R_(SER) and the transient circuit portion 54 basedon the open-circuit voltage V_(OC) for the given sample (k), as follows:V _(RC)(k)=V _(BAT)(k)−V _(OC)(k)  Equation 17To obtain the open-circuit voltage V_(OC)(k), the battery sensecontroller can implement the values of the previously calculatedopen-circuit voltage V_(OC)(k−1) and the previously estimated currentI_(EST)(k−1), stored in the previous battery data 22, as follows:V _(OC)(k)=I _(EST)(k−1)*Ts*C _(SER)(k)+V _(OC)(k−1)  Equation 18The open-circuit voltage V_(OC)(k) can also be adjusted for temperatureusing Equation 8 described above. Therefore, the battery sensecontroller 12 can estimate the current I_(EST)(k) generated by thebattery 14 as follows:I _(EST)(k)=P ₀ *V _(RC)(k)+P ₁ *V _(RC)(k−1)+P ₂ *I_(EST)(k−1)  Equation 19

Upon estimating the current I_(EST)(k) generated by the battery 14, thebattery sense controller 12 can also calculate the SOC of the battery 14at the sample time (k). Specifically, the battery sense controller 12can implement the previous value of the DOD(k−1) and the previouslyestimated current I_(EST)(k−1), as follows:DOD(k)=DOD(k−1)−I _(EST)(k−1)*Ts/Q _(MAX)  Equation 20SOC(k)=1−DOD(k)  Equation 21The SOC(k) can then be provided to an indicator (not shown) thatprovides an indication of the SOC of the battery 14 to a user of theassociated portable electronic device. The values of the DOD(k), theopen-circuit voltage V_(OC)(k), and the estimated current I_(EST)(k) canthen be provided to the memory 18 via the signal DATA_(BAT) to be storedas the previous battery data 22, such that the battery sense controller12 can recursively calculate the SOC of the battery at a future samplingtime (k+1). In addition, the resistance base variable R_A can be updatedin the memory 18 to account for changes in the battery resistanceR_(BAT) as the battery 14 ages.

Therefore, the SOC of the battery 14 can be accurately calculated basedon the voltage V_(BAT) and the temperature T of the battery 14. Such amanner of battery sensing is thus more accurate than a typical voltagecorrelation battery sensing method because the battery sensing describedherein accounts for an IR drop effect on the voltage V_(BAT) whilecurrent flows through the load. In addition, the manner of batterysensing described herein is also more cost effective and efficient thana typical coulomb counting battery sensing method because the batterysensing described herein does not require an additional current sensorto calculate the SOC of the battery 14. Accordingly, the battery sensingmethodology described herein is more accurate, cost effective, andefficient than typical battery sensing methodologies.

In view of the foregoing structural and functional features describedabove, a methodology in accordance with various aspects of the inventionwill be better appreciated with reference to FIG. 5. While, for purposesof simplicity of explanation, the methodology of FIG. 5 is shown anddescribed as executing serially, it is to be understood and appreciatedthat the invention is not limited by the illustrated order, as someaspects could, in accordance with the invention, occur in differentorders and/or concurrently with other aspects from that shown anddescribed herein. Moreover, not all illustrated features may be requiredto implement a methodology in accordance with an aspect of theinvention.

FIG. 5 illustrates an example of a method 200 for calculating a state ofcharge (SOC) of a battery in accordance with an aspect of the invention.At 202, the battery is modeled as a dynamic battery model comprising asteady-state circuit portion and a transient circuit portion todetermine predetermined data associated with steady-state and transientbehaviors of the battery relative to a DOD of the battery. The modelingof the battery can include determining values for resistors andcapacitors, as well as temperature dependent variables associated withvoltage and resistance of the battery, for each of a predeterminednumber of DOD values of the dynamic battery model. The dynamic batterymodel and associated test battery can have the same chemistry as thebattery for accurate modeling of the circuit parameters.

At 204, a temperature of the battery is determined. The temperature canbe determined based on a temperature sensor that monitors thetemperature of the battery or an ambient temperature of the batteryenvironment. At 206, a voltage of the battery is measured. At 208, thepredetermined data is accessed from a memory. The predetermined data canalso include previously calculated battery data, including a previouslycalculated DOD and estimated current. At 210, the SOC of the battery iscalculated based on the voltage, the predetermined data, and thetemperature. The calculation of the SOC can be based on the Equationsdescribed above.

What have been described above are examples of the invention. It is, ofcourse, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the invention,but one of ordinary skill in the art will recognize that many furthercombinations and permutations of the invention are possible.Accordingly, the invention is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims.

What is claimed is:
 1. A battery sense system comprising: a temperaturesensor configured to measure a temperature of a battery; a memoryconfigured to store predetermined data associated with steady-state andtransient behaviors of the battery relative to a depth of discharge(DOD) of the battery; and a controller configured to obtain samples of avoltage of the battery at each of a plurality of sampling intervals, toestimate, without requiring an additional current sensor, acorresponding current generated by the battery at a given samplinginterval k of the plurality of sample intervals wherein battery currentcan be determined both under operating conditions and passive conditionsbased only on the voltage at a respective one of the sampling intervals,the predetermined data, and the temperature, and to calculate a state ofcharge (SOC) of the battery based on based on the estimated currentthrough the battery at the respective one of the sampling intervals andbased on the DOD of the battery at an immediately preceding samplinginterval k-1.
 2. The system of claim 1, wherein the predetermined dataassociated with the steady-state and transient behaviors of the batteryare determined based on modeling the battery as a dynamic battery modelcomprising a steady-state circuit portion and a transient circuitportion, each of the static and transient circuit portions comprising atleast one RC network.
 3. The system of claim 1 wherein the estimate ofthe battery current at the present sample is based on a plurality ofprevious voltage samples.
 4. The system of claim 2, wherein at least aportion of the predetermined data associated with the steady-state andtransient behaviors of the battery is determined based on applying apredetermined load to the dynamic battery model and measuring a changein a voltage associated with the dynamic battery model as a function ofa current through the predetermined load.
 5. The system of claim 4,wherein at least a portion of the predetermined data associated with thesteady-state and transient behaviors of the battery is determined basedon measuring a voltage response associated with the dynamic batterymodel upon removing the predetermined load.